While copper or copper alloys excellent in electric conductivity have been used for electric contact parts for a long time, the number of cases of using naked copper or copper alloys is decreasing in recent years due to improvement of contact point characteristics, and materials prepared by applying various surface treatments on copper or copper alloys are being produced and used. In particular, the electric contact parts are often plated with noble metals for many uses as materials for electric contacts. Noble metals such as gold, silver, palladium, platinum, iridium, rhodium and ruthenium have been used for various electric contact materials due to their stability and excellent electric conductivity. In particular, silver has been widely used in many industrial fields since it is most excellent in electric conductivity among the metals and is relatively inexpensive among the noble metals. In addition, various materials have been produced by cladding electric contact parts with these noble metals.
Materials for electric contacts considered to be excellent in wear resistance have been used for electric contact parts that experience repeated insertion/desertion or sliding in recent years. These include connector terminals of harnesses in automobiles, contact switches mounted in portable phones, and terminals of memory cards and PC cards. With respect to improvement in wear resistance, materials for contacts using hardened silver and hardened gold have been commonly used for a general purpose. Other examples of research and development include clad materials and plated materials in which micro-particles are dispersed, and various surface-treated materials have been developed for improving sliding characteristics of the materials for electric contacts. For example, JP-A-03-191084 (“JP-A” means unexamined published Japanese patent application) has attempted to improve wear resistance and corrosion resistance by covering a nickel plating as a underlayer, a palladium plating as an intermediate layer, and a gold plating as a top layer, on a copper base material having a given hardness and surface toughness, wherein the Vickers hardness and surface roughness (Rz) of the base material are adjusted to be 230 or less and 45 μm or less, respectively, while the plating layers are composed of a semi-bright or matte nickel plating with a thickness of 3.0 μm or less as the intermediate layer, a bright palladium or bright palladium-nickel alloy plating with a thickness of 1.5 μm or less as the intermediate layer, and a gold or gold alloy plating with a thickness from 0.1 to 0.5 μm.